1. Field of the Invention
The present invention relates to an electronic system which may be mounted in an automotive vehicle for avoiding noise, especially interference noise generated from a plurality of digital processing units constituting microcomputers incorporated in the electronic system, from disturbing, external communication equipment, such as a radio set mounted in the same automotive vehicle, from receiving a broadcast signal.
2. Description of the Prior Art
In recent years, with the rapid growth of the electronics technology, a plurality of microcomputers are being mounted in automotive vehicles for controlling operations of the associated internal combustion engines or various electrical devices. Rectangular or other shape clock pulses having frequencies of several hundred KHz to several MHz, are commonly used for timing signals for microcomputer operation. The clock pulses may comprise a fundamental of a relatively large magnitude (several volts) and harmonic components, the frequencies of which range through a considerable portion of the broadcast frequency spectrum, from the amplitude modulating broadcasting frequencies (the AM band) through the television channel frequencies (VHF and UHF bands) to the frequency modulated broadcasting frequencies (FM band). Therefore, the rectangular clock pulse can function as a noise source with regard to the receivers. These broadcast frequency noise components are fed into the I/O signal lines and power line of the microcomputer, a radio set or other receiver in the vehicle may suffer interference due to direct or indirect coupling of the radio harness of the radio antenna with the I/O signal lines and power line.
Experiments have revealed that when a plurality of microcomputers are mounted in the same vehicle and the frequencies of the harmonic components of the rectangular clock pulses used in the microcomputers are close and are in the FM broadcasting band, an extremely high level of interference will be produced if the plurality of microcomputers are operated simultaneously because of interference between the harmonic components from each of the clock pulses.
In order to prevent the noise components causing this disturbance from leaking out of the I/O signal and power lines, it is necessary, especially in the high frequency band, to completely isolate that part of each microcomputer which is operated by the clock pulse from that part which is not operated by the clock pulse. However, this is not practical, either technically or economically.
There are two additional ways for preventing electromagnetic coupling between the signal lines, into which the noise components from the clock pulses are leaked, to the radio harness and the antenna.
(a) Shielded wires such as coaxial cables may be used for all or part of the signal lines; or PA1 (b) The signal lines may be wired separately from the radio harness or the antenna.
However, neither of these alternatives is practical when there are a large number of signal lines and the wiring of the signal lines becomes very complicated, or when the signal lines are distributed over almost the entire automotive vehicle body.